LED print bars used in a variety of printing systems must be moved away from a photoreceptor for cleaning/maintenance operations and during replacement. When the print bar is returned to its operating position, it must be restored to substantially its original position relative to the x, y and z planes or directions, and by extension relative to the photoreceptor. For example, a LED print bar including a SELFOC® lens arranged to focus an image on the photoreceptor must be positioned typically within +/−50 microns of its ideal location in order to satisfy image quality requirements, as SELFOC® lenses typically have very short focal lengths. Unfortunately, typical or known mechanical arrangements rely upon mechanisms that can constrain the LED print bar thereby restricting accurate positioning of the print bar, e.g., print bars become bound in a tilted orientation thereby effecting the alignment and position of the print bar relative to the photoreceptor.
Known print bar locating means include some x and y direction degrees of freedom. However, such systems fail to also control the critical positioning in the z direction, i.e., the distance between the SELFOC® lens and the photoreceptor. Failing to accurately control the z plane prevents the proper focusing of an image on the photoreceptor thereby degrading image quality.
In short, known systems may position the print bar in some directions; however, those systems do not permit relaxed tolerances on components used for position control, and do not permit unassisted settling of the print bar within a system used to align and position the print bar relative to the photoreceptor.
In some known systems, the LED print bar has features which allow x and y direction positioning via a hole at one end of the print bar and a slotted hole at the other end, and the mount has a small amount of x and y direction freedom to accommodate pick-up on the location features and subsequent datum location. However if the LED print bar is held firmly in a mount mechanism, the angle of the mount mechanism relative to the datum pins may cause the print bar to not settle correctly on the z datum surface resulting in an inaccuracy in the positioning of the LED print bar relative to the photoreceptor, e.g., a drum surface, and subsequent focus degradation. Moreover, simply providing the mount more freedom of movement may not cause it to pick up on the locating pins or, because of the mount and print bar's high mass, may not settle on the z datum surface reliably.
FIGS. 1 and 2 depict known systems for locating LED print bar 50 relative to photoreceptor 52. FIG. 1 depicts the proper seating or positioning of print bar 50. Pin assembly 54 includes pin datum surfaces 56 and 58, while print bar 50 includes LED datum surfaces 60 and 62. Pin 64 is positioned within opening 66 in print bar 50 such that pin datum surface 56 fully contacts LED datum surface 60 and pin datum surface 58 fully contacts LED datum surface 62. Thus, pin controlled distance 68 is properly established. It should be appreciated that pin controlled distance 68 is the distance from front surface 70 of print bar 50 to pin feature 72, e.g., a mounting surface. Pin feature 72 in turn locates off of a feature (not shown) which is associated with photoreceptor 52, e.g., a bearing or a mounting structure. The foregoing arrangement controls the critical distance between front surface 74 of SELFOC® lens 76 and photoreceptor 52, i.e., distance 78.
The foregoing system is unfortunately prone to misalignment resulting in the condition depicted in FIG. 2. When print bar 50 is positioned about pin 64, tilt of print bar 50 results in improper alignment of LED datum surfaces 60 and 62 and pin datum surfaces 56 and 58. The foregoing condition results in a change to the critical distance between front surface 74 of SELFOC® lens 76 and photoreceptor 52, i.e., distance 80 shown in FIG. 2 is greater than the ideal distance 78 shown in FIG. 1. It should be appreciated that tilt in the opposite direction is also possible and would result in distance 80 being less than distance 78. As can be seen in FIG. 2, when LED print bar 50 does not sit on both pin datums 56 and 58, a change in from distance 78 to distance 80 occurs, i.e., a change in the critical print bar to photoreceptor distance. The foregoing defect can occur if LED print bar 50 is constrained in its mount (not shown) as the mount has a fixed pivot point relative to its frame (not shown) (See FIG. 3 for an example of a mount relative to a frame). If pin datums 56 and 58 on pin 64, i.e., the pin responsible for aligning the print bar in the x and y directions, are not both engaged with print bar datums 60 and 62, respectively, print bar 50 will not be at the correct angle and hence distance 80 is greater than distance 78. In order to maintain acceptable image focus on the photoreceptor, and thereby printing performance, distance 78 must be controlled within or better than +/−50 um.
The present disclosure addresses all these problems in a practical and cost effective method.